linux-kernel - Re: [RFC PATCH 1/2] ceph: add support for encrypted snapshot names

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Message-ID: <2d69e6dd-b047-13fe-7dc5-2c64190e0e8a@redhat.com>
Date:   Mon, 14 Mar 2022 10:45:46 +0800
From:   Xiubo Li <xiubli@...hat.com>
To:     Luís Henriques <lhenriques@...e.de>,
        Jeff Layton <jlayton@...nel.org>,
        Ilya Dryomov <idryomov@...il.com>
Cc:     ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] ceph: add support for encrypted snapshot names


On 3/12/22 4:30 PM, Xiubo Li wrote:
>
> On 3/11/22 1:26 AM, Luís Henriques wrote:
>> Since filenames in encrypted directories are already encrypted and shown
>> as a base64-encoded string when the directory is locked, snapshot names
>> should show a similar behaviour.
>>
>> Signed-off-by: Luís Henriques <lhenriques@...e.de>
>> ---
>>   fs/ceph/dir.c   |  9 +++++++++
>>   fs/ceph/inode.c | 13 +++++++++++++
>>   2 files changed, 22 insertions(+)
>>
>> diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
>> index 6df2a91af236..123e3b9c8161 100644
>> --- a/fs/ceph/dir.c
>> +++ b/fs/ceph/dir.c
>> @@ -1075,6 +1075,15 @@ static int ceph_mkdir(struct user_namespace 
>> *mnt_userns, struct inode *dir,
>>           op = CEPH_MDS_OP_MKSNAP;
>>           dout("mksnap dir %p snap '%pd' dn %p\n", dir,
>>                dentry, dentry);
>> +        /*
>> +         * Encrypted snapshots require d_revalidate to force a
>> +         * LOOKUPSNAP to cleanup dcache
>> +         */
>> +        if (IS_ENCRYPTED(dir)) {
>> +            spin_lock(&dentry->d_lock);
>> +            dentry->d_flags |= DCACHE_NOKEY_NAME;
>
> I think this is not correct fix of this issue.
>
> Actually this dentry's name is a KEY NAME, which is human readable name.
>
> DCACHE_NOKEY_NAME means the base64_encoded names. This usually will be 
> set when filling a new dentry if the directory is locked. If the 
> directory is unlocked the directory inode will be set with the key.
>
> The root cause should be the snapshot's inode doesn't correctly set 
> the encrypt stuff when you are reading from it.
>
> NOTE: when you are 'ls -l .snap/snapXXX' the snapXXX dentry name is 
> correct, it's just corrupted for the file or directory names under 
> snapXXX/.
>
When mksnap in ceph_mkdir() before sending the request out it will 
create a new inode for the snapshot dentry and then will fill the 
ci->fscrypt_auth from .snap's inode, please see 
ceph_mkdir()->ceph_new_inode().

And in the mksnap request reply it will try to fill the ci->fscrypt_auth 
again but failed because it was already filled. This time the auth info 
is from .snap's parent dir from MDS side. In this patch in theory they 
should be the same, but I am still not sure why when decrypting the 
dentry names in snapXXX will fail.

I just guess it possibly will depend on the inode number from the 
related inode or something else. Before the request reply it seems the 
inode isn't set the inode number ?

- Xiubo

>
>> + spin_unlock(&dentry->d_lock);
>> +        }
>>       } else if (ceph_snap(dir) == CEPH_NOSNAP) {
>>           dout("mkdir dir %p dn %p mode 0%ho\n", dir, dentry, mode);
>>           op = CEPH_MDS_OP_MKDIR;
>> diff --git a/fs/ceph/inode.c b/fs/ceph/inode.c
>> index b573a0f33450..81d3d554d261 100644
>> --- a/fs/ceph/inode.c
>> +++ b/fs/ceph/inode.c
>> @@ -182,6 +182,19 @@ struct inode *ceph_get_snapdir(struct inode 
>> *parent)
>>       ci->i_rbytes = 0;
>>       ci->i_btime = ceph_inode(parent)->i_btime;
>>   +    /* if encrypted, just borrow fscrypt_auth from parent */
>> +    if (IS_ENCRYPTED(parent)) {
>> +        struct ceph_inode_info *pci = ceph_inode(parent);
>> +
>> +        ci->fscrypt_auth = kmemdup(pci->fscrypt_auth,
>> +                       pci->fscrypt_auth_len,
>> +                       GFP_KERNEL);
>> +        if (ci->fscrypt_auth) {
>> +            inode->i_flags |= S_ENCRYPTED;
>> +            ci->fscrypt_auth_len = pci->fscrypt_auth_len;
>> +        } else
>> +            dout("Failed to alloc memory for fscrypt_auth in 
>> snapdir\n");
>> +    }
>
> Here I think Jeff has already commented it in your last version, it 
> should fail by returning NULL ?
>
> - Xiubo
>
>>       if (inode->i_state & I_NEW) {
>>           inode->i_op = &ceph_snapdir_iops;
>>           inode->i_fop = &ceph_snapdir_fops;
>>